The principal causes of myocardial cell death following insult are not established. The main objectives of this project are to determine the factors that produce mitochondrial dysfunction in the acutely ischemic myocardium. The fundamental mechanisms involving ATP production and calcium transport in heart mitochondria will be studied with a particular focus on calcium retention and release. An in vitro model is used to alter calcium transport kinetics in normal heart mitochondria by depletion of internal adenine nucleotides. These mitochondria resemble those obtained from acutely ischemic hearts. Isolated, adult myocytes will also be used as an in vitro model in an attempt to "bridge the gap" between observed changes in the mitochondrial model and that of the intact heart. The role of the adenylate cyclase system will be simultaneously studied. Spectrophotometric and radioisotope techniques will be used to monitor calcium transport, adenine nucleotide fluxes and membrane changes. Multi-parameter measurements using ion selective electrodes in conjunction with the spectrophotometric techniques will be used to gain an integrated picture of mitochondrial function from normal and ischemic hearts. The major hypothesis to be tested is that the primary cause of myocardial cell death involves selective membrane damage and that this damage is related to altered energy metabolism. An understanding of the primary causes of altered heart cell function can subsequently be utilized to develop specific therapeutic interventions to reduce myocardial damage and preserve function following a heart attack.